E. Zeyhle

Portable ultrasound scanner versus serology in screening for hydatid cysts in a nomadic population

3553 nomads in Turkana, a remote area of north-west Kenya, were screened for hydatid cysts by a portable ultrasound scanner and by serology. 198 (5.6%) proved to have liver or upper abdominal cysts. In the group screened by both techniques (2644) 174 (6.6%) cases of hydatidosis were detected by ultrasonography and 76 (2.9%) by serology. Ultrasonography gave immediate results and was less expensive and more acceptable and educationally valuable to the people. This non-invasive rapid technique also provided important clinical information about the cysts. The prevalence data thus obtained will contribute to the surveillance of a hydatid control programme.

Pastoralists and hydatid disease: an ultrasound scanning prevalence survey in East Africa

An attempt was made to estimate the prevalence of hydatid disease in nomadic pastoralists living in eastern Africa and to identify environmental, cultural and behavioural factors which may influence Echinococcus transmission. 18,565 nomadic pastoralists, from 12 different groups living in the vast, semi-desert regions of Kenya, Sudan, Ethiopia and Tanzania, were screened for hydatid cysts using a portable ultrasound scanner. High prevalences of hydatidosis were recorded among the north-western (5.6%) and north-eastern (2.1%) Turkana of north-west Kenya, the Toposa (3.2%) of southern Sudan, the Nyangatom (2.2%), Hamar (0.5%) and Boran (1.8%) of south-west Ethiopia and northern Kenya and the Maasai (1.0%) of Tanzania. Lower prevalences were recorded amongst the southern (0.3%) and lake dwelling (0.3%) Turkana and the Pokot (0.1%) of Kenya. The disease was not found amongst the Turkana, Samburu, Dassanetch, Gabbra, Somali or Rendille screened on the east side of Lake Turkana. The scanning surveys were well accepted by the people and provided evidence for the need to expand the present hydatid control programme in Turkana to cover the whole hyperendemic focus. Such a programme must contain an educational component for, although most groups recognized hydatid cysts, there was complete lack of knowledge concerning the parasite and its mode of transmission.

A study of cystic echinococcosis in slaughter animals in three selected areas of northern Turkana, Kenya.

In an attempt to establish the prevalence of cystic echinococcosis, a study was conducted in slaughter animals in three divisions of northern Turkana, Kenya. A total of 5752 goats, 588 sheep, 381 cattle and 70 camels were examined at slaughter. Echinococcus granulosus metacestodes were found in 19.4% of the cattle, 3.6% of sheep, 4.5% of goats and 61.4% of camels. The prevalence of cystic echinococcosis in cattle, sheep and goats was higher in Lokichogio than in either Kakuma or Central divisions. On the other hand, the prevalence of the disease in camels was higher in Central (84.6%) than either Lokichogio (70.6%) or Kakuma (50%). The differences in prevalence rates in different study areas are attributed to differences in environmental conditions, livestock stocking intensity and cross-border migration of livestock.

Hydatid disease: research and control in Turkana. II. The role of immunological techniques for the diagnosis of hydatid disease.

Immunological studies have been applied to the immunodiagnosis of human hydatidosis in Turkana and for the specific identification of Echinococcus eggs, particularly in regard to their potential for the assessment of a hydatid control programme in the north-west of the District. A high rate of false negatives has been obtained with sensitive antibody tests for proven hydatid patients in Turkana and presents problems for prevalence estimation in the population. A seroepidemiological study using specific antibody detection indicated a 2·17% seropositive rate, and by using a portable ultrasound 67% of antibody positives were confirmed as having liver/abdominal cysts. An enzyme immunoassay test for specific circulating antigen, often associated with circulating immune complexes, was positive in sera in 75% of hydatid patients who were antibody-negative. The formation of specific circulating immune complexes may contribute directly to the production of a state of false negativity. These studies indicate that by combining tests for antibodies and antigens together with ultrasound, the true prevalence of human hydatidosis in Turkana is at least 5%. Characterization of Echinococcus antigens recognized by human antisera from Turkana and British hydatid patients indicates that both groups recognize the same major protein antigens in cyst fluid and protoscoleces. The results of assaying anti-oncospheral antibodies in people living in the high prevalence area of north-west Turkana compared to people in areas of low prevalence indicates that most of the people in the high prevalence area are probably infected (challenged) with Echinococcus eggs. This observation suggests that there may be a high level of acquired resistance. A species-specific immunofluorescence test using an anti-Echinococcus monoclonal antibody has been developed which can specifically identify oncospheres artificially hatched from Echinococcus eggs. This test will be applied to the problem of identification of Echinococcus eggs in the environment and in dog faeces, with a view to studying the epidemiology of the disease and for use in assessment of the hydatid control programme.Immunological studies have been applied to the immunodiagnosis of human hydatidosis in Turkana and for the specific identification of Echinococcus eggs, particularly in regard to their potential for the assessment of a hydatid control programme in the north-west of the District. A high rate of false negatives has been obtained with sensitive antibody tests for proven hydatid patients in Turkana and presents problems for prevalence estimation in the population. A seroepidemiological study using specific antibody detection indicated a 2.17% seropositive rate, and by using a portable ultrasound 67% of antibody positives were confirmed as having liver/abdominal cysts. An enzyme immunoassay test for specific circulating antigen, often associated with circulating immune complexes, was positive in sera in 75% of hydatid patients who were antibody-negative. The formation of specific circulating immune complexes may contribute directly to the production of a state of false negativity. These studies indicate that by combining tests for antibodies and antigens together with ultrasound, the true prevalence of human hydatidosis in Turkana is at least 5%. Characterization of Echinococcus antigens recognized by human antisera from Turkana and British hydatid patients indicates that both groups recognize the same major protein antigens in cyst fluid and protoscoleces. The results of assaying anti-oncospheral antibodies in people living in the high prevalence area of north-west Turkana compared to people in areas of low prevalence indicates that most of the people in the high prevalence area are probably infected (challenged) with Echinococcus eggs. This observation suggests that there may be a high level of acquired resistance. A species-specific immunofluorescence test using an anti-Echinococcus monoclonal antibody has been developed which can specifically identify oncospheres artificially hatched from Echinococcus eggs. This test will be applied to the problem of identification of Echinococcus eggs in the environment and in dog faeces, with a view to studying the epidemiology of the disease and for use in assessment of the hydatid control programme.

Echinococcosis in sub-Saharan Africa: emerging complexity.

Cystic echinococcosis occurs in most regions of sub-Saharan Africa, but the frequency of this zoonosis differs considerably among and within countries. Especially human cases seem to be focally distributed. A number of environmental and behavioural factors partially explain this pattern, i.e. density of livestock, presence of dogs, uncontrolled slaughter, and hygiene. In addition, the various taxa of Echinococcus spp. are known to differ considerably in infectivity to different host species including humans. Genetic characterizations of isolates, which are necessary to evaluate the impact of this factor - so far done in only a few countries - indicate that the diversity of Echinococcus spp. in Sub-Saharan Africa is greater than on any other continent. The very incomplete data which are available show that sympatrical taxa may infect different hosts, others may be geographically restricted, some life cycles involve livestock, others wild animals. Possible implications of this complexity for public health, livestock economy and conservation are briefly discussed.

Molecular evidence of the camel strain (G6 genotype) of Echinococcus granulosus in humans from Turkana, Kenya

Cystic echinococcosis (CE) is a zoonotic helminthic disease, which is widely distributed throughout the world. Although G1 is the Echinococcus granulosus genotype most commonly involved in CE in humans, the prevalence of infection with other genotypes, such as G6, may be higher than previously thought. We performed molecular analysis to identify which E. granulosus genotypes are the causative agents of CE in humans in Kenyas Turkana district. During a Hydatid Control Programme in 1993-1994, 71 cyst fluid isolates of E. granulosus were collected during PAIR (puncture, aspiration, injection, re-aspiration) sessions. DNA was amplified for two genes from 59 isolates. Of these, 49 isolates (83%) were identified as G1 and 10 (17%) as G6. This is the highest prevalence of G6 detected in humans of the Old World, and our results suggest that, in highly contaminated environments, G6 might be of greater public health significance than previously believed.

Cystic echinococcosis in sub-Saharan Africa

Cystic echinococcosis is regarded as endemic in sub-Saharan Africa; however, for most countries only scarce data, if any, exist. For most of the continent, information about burden of disease is not available; neither are data for the animal hosts involved in the lifecycle of the parasite, thus making introduction of preventive measures difficult. Available evidence suggests that several species or strains within the Echinococcus granulosus complex are prevalent in sub-Saharan Africa and that these strains might be associated with varying virulence and host preference. Treatment strategies (chemotherapy, percutaneous radiological techniques, but mainly surgery) predominantly target active disease. Prevention strategies encompass anthelmintic treatment of dogs, slaughter hygiene, surveillance, and health-educational measures. Existing data are suggestive of unusual clinical presentations of cystic echinococcosis in some parts of the continent, for which the causes are speculative.

Hydatid disease: Research and control in Turkana, IV. The pilot control programme

A pilot programme to control hydatid disease in north-west Turkana district was started in October 1983 with an intensive educational campaign. This was followed by control and treatment of the dog population to reduce the prevalence of Echinococcus granulosus, thereby reducing the infective pressure on man. Surveillance is by mass annual sero-epidemiological and ultrascan surveys of the nomadic Turkana within the control region and by arecoline purging of the dogs. Some of the recent advances in research on hydatid disease in subject areas such as immunodiagnosis, chemotherapy and epidemiology have been incorporated into the present programme, and their relevance to this and other similar programmes is discussed.

Evaluation of diagnostic ultrasound as a mass screening technique for the detection of hydatid cysts in the liver and lung of sheep and goats

Ultrasound examination of the liver and lung followed by post-mortem examination was performed in 16 sheep and 284 goats. Thirty-one (10.3%) were positive for hydatid cysts on ultrasound examination and 46 (15.3%) were positive on post-mortem examination. Twenty-one positive on post-mortem examination were falsely identified as negative on ultrasound examination. Of the 254 animals negative on post-mortem examination, six (2.4%) were falsely identified as positive on ultrasound examination. The sensitivity and specificity of ultrasound examination for detecting hydatid cysts in sheep and goats was 54.36% and 97.64%, respectively (positive predictive value: 80.64%; negative predictive value: 92.19%).

Assessment of a serological test for the detection of Echinococcus granulosus infection in dogs in Kenya

Specific diagnosis of Echinococcus granulosus infection in dogs has played a significant role in implementing hydatid control programs. Most programs have relied on purging dogs with arecoline hydrobromide and examining purge samples for worms to diagnose infection. This technique is time consuming and suffers from limitations including poor sensitivity, particularly in dogs with light infections, risk of hydatid infection to control personnel and severe side-effects of the arecoline in some dogs. Also, availability of praziquantel in several countries has further limited the value of the technique as owners can treat their dogs to eliminate worms prior to presenting them for purging. Application of a simple and sensitive immunological or serological detection system would overcome these problems and be a useful adjunct in control programs. Reports have described alternative techniques which show promise for accurate diagnosis of E. granulosus infection in the definitive host (Jenkins and Rickard, 1985, 1986; Craig et al., 1988). Recently, an enzyme-linked immunosorbent assay (ELISA) using E. granulosus protoscolex antigen was developed (Gasser et al., 1988), and its sensitivity was higher than the level achieved in studies using arecoline testing (Gemmell, 1968; Trejos et al., 1975). The aim of the present study was to assess the performance of the ELISA in an endemic area of Kenya for detecting dogs with E. granulosus infection, and comparing serological data with parasitological data obtained from the dogs by necropsy. Dogs shot in north-western Turkana (Oropoi, Nanam, Lokichoggio, Lakankai,